Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

2. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

One heat exchanger

Four heat exchangers

3. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

4. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

5. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

Takes place at constant entropy

6. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 3

1: 9

1: 1

7. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

5 tons

40 tons

8. For obtaining high COP, the pressure range of compressor should be

Low

Optimum

Any value

High

9. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

10. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

Page 2 of 4

11. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-135.8°C

-56.6°C

12. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

13. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

14. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

15. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

16. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

1.33

2.33

17. The domestic refrigerator uses following type of compressor

Centrifugal

Axial

Piston type reciprocating

Miniature sealed unit

18. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Brine

Carbon dioxide

Freon

19. Most thermostatic expansion valves are set for a superheat of

15°C

20°C

10°C

5°C

20. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Inflammable

Non-inflammable and toxic

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21. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Carnot

Reversed Carnot

22. The boiling point of ammonia is

-33.3°C

-10.5°C

-77.7°C

-30°C

23. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

24. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

25. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always less than unity

Always more than unity

Any one of the above

26. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

27. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

30 bar

8 bar

2 bar

28. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

29. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.376

0.6

30. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

Page 4 of 4

31. Which of the following cycles uses air as the refrigerant?

Stirling

Bell Coleman

Ericson

Carnot

32. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

33. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

34. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Sub-cooling or under-cooling

Normal cooling

Super-cooling

35. The capillary tube, as an expansion device, is used in

Room air conditioners

Domestic refrigerators

All of these

Water coolers

36. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

Low boiling point

High risibility with oil

37. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

38. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

39. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

None of these

Zero

Negative

40. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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